<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="jquery-3.4.1.js"></script>
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
    </ul>
    <button>按钮</button>
    <script>
        var colorArr=['red','green','bule']
        $('button').click(function(){
            $('li').each(function(index,dom){
                $(dom).css('background',colorArr[index]);
            })

            $.each(colorArr,function(index,item){
                console.log(index,item);
            })
        })
       
    </script> 
</body>
</html>